feat: add `ReceiveAddressQR` component using `qrcode.react`

[rayeberechi]

Summary

Users need a way to display their Stellar public key as a QR code for easy scanning. This component wraps qrcode.react and adds a copy button.

Implementation Steps

1. Discuss adding qrcode.react as a dependency in this issue before merging — it must be approved by a maintainer.
2. Create src/components/common/ReceiveAddressQR.tsx.
3. Props: address: string, size?: number (default 200), className?: string, showCopyButton?: boolean (default true).
4. Render <QRCodeSVG value={address} size={size} /> from qrcode.react.
5. If showCopyButton is true, render a <CopyableAddress address={address} /> below the QR code.
6. Wrap the whole component in a <figure> with <figcaption> showing the truncated address for screen readers.
7. Export from src/index.ts.
8. Write tests: renders SVG element; renders copy button when showCopyButton=true; hides copy button when false.

Definition of Done

• QR code renders as SVG.
• Copy button conditionally rendered.
• Accessible <figure> / <figcaption> structure.
• Dependency approved and pinned to exact version.
• Tests pass.